Characterization of trace element distributions in soils

摘要

A method was developed for the analysis of the trace element content of soils using X-ray fluorescence spectrometry (XRFS). The method was successfully applied to the determination of the distributions of Cr, Ni, Zn, Rb, Sr, Y, Zr, Pb, Ba, and Mn in several types of soils. Soils were fractionated into eight particle size fractions using sieves with meshes between 5 mum and 800 mum. We found that the studied elements were mostly concentrated in the smallest size fraction. Mineralogical phase analysis was carried out using X-ray powder diffraction (XRD), and the elemental compositions of solid soil samples were analyzed using XRFS method. Despite their variability, grain size distributions of different soils share some general features. Commonly the grains in the < 5 and 20-45-m fractions were most abundant. The trace elements occur in three types of associations: (a) adsorbed onto mineral surfaces; (b) in crystallographic positions within minerals (e.g. Ti in rutile, Zr in zircon); and (c) bound to clay minerals. Our results shaw that the grain size distribution of a given mineral is related to its origin and can be used as a source of information when soil-forming processes are studied. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 5]